This invention relates to a foundation system for tension leg platforms where tendons are anchored directly to sockets fitted inside the piles thereby doing away with the need to make use of rigid structures known as foundation templates.
Various kinds of anchoring pile systems for tension leg platformsxe2x80x94TLPsxe2x80x94are known. In all of them transfer of the anchored load to the piles is achieved by means of a structure in the sea bottom, known as a foundation template. This template has cylindrically shaped guides into which are driven tubular piles which are fixed to the foundation template either by cementing the annular space between the cylindrically shaped guide and the pile, or by deforming the steel of the pile with the aid of a tool which expands it against the guide, thereby bringing about a mechanical connection between the pile and the guide.
U.S. Pat. No. 4,620,820 illustrates a foundation system such as the one described above and discloses equipment and an anchoring system for a tension leg platform anchored to the sea bottom by means of an anchoring assembly made up of upper and lower parts. The upper part thereof is tied to the bottom ends of the tendons forming the tension legs of the tension leg platform. The upper part of the anchoring assembly serves to space out and line up each tendon, keeping them straight when the upper part of the assembly is joined to the lower part which has first of all been fixed to the sea bottom by means of the piles.
The foundation templates have to withstand cycles of heavy strain and must therefore be designed to withstand the ensuing fatigue which inevitably leads to their being sturdily and heavily built, thereby increasing the anchoring cost. Another critical point is that the joining of piles to the templates is prone to failure.
The invention described and claimed herein introduces significant modifications in such a system, does away with the need for templates in the foundations, cuts down on the cost of anchoring and considerably reduces the likelihood of failure since there are fewer mechanical parts.
For the purpose of principally doing away with the need for foundation templates, thus diminishing the cost of materials and the installation costs, this invention provides a tension leg platform foundation system wherein each tendon is directly connected to its pile by means of a socket fitted into the pile, the piles being driven in with the aid of a template which also serves to keep the piles apart from the template for the wells as they are positioned by means of pins that slot into guides fitted into the well-drilling template. After piles have been driven to anchor down one corner of the platform the template is withdrawn, and repositioned, so as to enable the piles for the other tendons to be driven, this procedure is repeated until all the piles have been driven.
The pile-driving template can also be built so as to serve as a guide for all of the piles thereby doing away with the need to reposition the template after each group of piles has been driven.